Search Results (4)

The substrate-induced respiration-inhibition (SIRIN) method has been used to estimate fungi-derived N₂O emissions, but its contribution to soil N₂O emissions remains unclear. There is a need to quantify the fungal fraction of N₂O production more precisely. Here, using isotopocule analysis, we assessed the relative contribution of fungi to soil N₂O production potential under denitrifying conditions, where key limiting factors of denitrification (soil moisture, soil NO₃⁻, and electron donor) were removed. The result showed that the ratio of fungi-derived N₂O emissions (R_F) was 0.83~4.28% in paddy soils, 13.80~23.21% in vineyard soils, and 15.34~65.94% in vegetable field soils, respectively. This indicated that the bacteria were the dominator of soil N₂O production potential in most cases, but fungal pathways could be significant in vegetable field soils. The experiment with bactericide addition showed that inhibitors could affect non-target microorganisms in the SIRIN method. Our further analyses suggest that it is worth to explore the effect of soil organic carbon and microbial synergies on fungi-derived N₂O emissions. Full article

Returning crop residues to agricultural fields can accelerate nutrient turnover and increase N₂O and NO emissions. Increased microbial respiration may lead to formation of local hotspots with anoxic or microoxic conditions promoting denitrification. To investigate the effect of litter quality on CO₂, NO, N₂O, and N₂ emissions, we conducted a laboratory incubation study in a controlled atmosphere (He/O₂, or pure He) with different maize litter types (Zea mays L., young leaves and roots, straw). We applied the N₂O isotopocule mapping approach to distinguish between N₂O emitting processes and partitioned the CO₂ efflux into litter- and soil organic matter (SOM)-derived CO₂ based on the natural ¹³C isotope abundances. Maize litter increased total and SOM derived CO₂ emissions leading to a positive priming effect. Although C turnover was high, NO and N₂O fluxes were low under oxic conditions as high O₂ diffusivity limited denitrification. In the first week, nitrification contributed to NO emissions, which increased with increasing net N mineralization. Isotopocule mapping indicated that bacterial processes dominated N₂O formation in litter-amended soil in the beginning of the incubation experiment with a subsequent shift towards fungal denitrification. With onset of anoxic incubation conditions after 47 days, N fluxes strongly increased, and heterotrophic bacterial denitrification became the main source of N₂O. The N₂O/(N₂O+N₂) ratio decreased with increasing litter C:N ratio and C_org:NO₃⁻ ratio in soil, confirming that the ratio of available C:N is a major control of denitrification product stoichiometry. Full article

Isotopocule signatures of N₂O (δ¹⁵N^bulk, δ¹⁸O and site preference) are useful for discerning soil N₂O source, but sometimes, N fertilizer is needed to ensure that there is enough N₂O flux for accurate isotopocule measurements. However, whether fertilizer affects these measurements is unknown. This study evaluated a gradient of NH₄NO₃ addition on N₂O productions and isotopocule values in two acidic subtropical soils. The results showed that N₂O production rates obviously amplified with increasing NH₄NO₃ (p < 0.01), although a lower N₂O production rate and an increasing extent appeared in forest soil. The δ¹⁵N^bulk of N₂O produced in forest soil was progressively enriched when more NH₄NO₃ was added, while becoming more depleted of agricultural soil. Moreover, the N₂O site preference (SP) values collectively elevated with increasing NH₄NO₃ in both soils, indicating that N₂O contributions changed. The increased N₂O production in agricultural soil was predominantly due to the added NH₄NO₃ via autotrophic nitrification and fungal denitrification (beyond 50%), which significantly increased with added NH₄NO₃, whereas soil organic nitrogen contributed most to N₂O production in forest soil, probably via heterotrophic nitrification. Lacking the characteristic SP of heterotrophic nitrification, its N₂O contribution change cannot be accurately identified yet. Overall, N fertilizer should be applied strictly according to the field application rate or N deposition amount when using isotopocule signatures to estimate soil N₂O processes. Full article

Paddies are a potential source of anthropogenic nitrous oxide (N₂O) emission. In paddies, both the soil and the rice plants emit N₂O into the atmosphere. The rice plant in the paddy is considered to act as a channel between the soil and the atmosphere for N₂O emission. However, recent studies suggest that plants can also produce N₂O, while the mechanism of N₂O formation in plants is unknown. Consequently, the rice plant is only regarded as a channel for N₂O produced by soil microorganisms. The emission of N₂O by aseptically grown plants and the distinct dual isotopocule fingerprint of plant-emitted N₂O, as reported by various studies, support the production of N₂O in plants. Herein, we propose a potential pathway of N₂O formation in the rice plant. In rice plants, N₂O might be formed in the mitochondria via the nitrate–nitrite–nitric oxide (NO₃–NO₂–NO) pathway when the cells experience hypoxic or anoxic stress. The pathway is catalyzed by various enzymes, which have been described. So, N₂O emitted from paddies might have two origins, namely soil microorganisms and rice plants. So, regarding rice plants only as a medium to transport the microorganism-produced N₂O might be misleading in understanding the role of rice plants in the paddy. As rice cultivation is a major agricultural activity worldwide, not understanding the pathway of N₂O formation in rice plants would create more uncertainties in the N₂O budget. Full article